Cellulose composition material



Patented June 16, 1942 CELLULOSE CODIPOSITION MATERIAL Ralph H. McKee,New York, N. Y.

No Drawing. Application March 4, 1938, Serial No. 193,921

14 Claims. (Cl. 106-473) This invention relates to an improved plasti-'cizable mixture which is initially moldable, which is especiallyadapted to take fine imprints and impressions from copy plates andreliefs, and

when hardened or solidified into a film or sheet, is serviceable in theprinting, graphic and reproduction arts as a printing plate havingprinting impressions in the surface thereof. The present application isa continuation-in-part of my prior application Serial No. 559,778, filedAugust 27, 1931, issued on May 10, 1938, as Patent No. 2,116,- 536.

The plastic material which I have invented possesses suchcharacteristics as make it especially valuable for use in the printing,graphic and reproduction arts. The finished product herein disclosedwill take a sharp, clear and accurate impression of surfaces, such ascopy reliefs, when the composition is pressed forcibly into contacttherewith and allowed to harden and set. In addition, the product doesnot shrink upon hardening or with age, is free from plastic flow, issubstantially non-thermoplastic and accurately and uniformly retains itsoriginal surface shape and contour. The product as herein disclosed willnot adhere to a dampened or water swollen gelatine copy relief, and,therefore, constitutes and excellent material for printing plates whichcan be cast from such a copy relief. When fully solidified, the improvedproduct of the present invention is hard, tough, durable and wearresisting and is especially useful and valuable in situations where sucha material is desired.

The printing plates are made and cast from my improved compositionsubstantially as follows: Using the screens and photographic apparatuscustomary in the printing industry, a positive (if intaglio), ornegative (if half tone or relief) is taken on a gelatine plate(generally backed with celluloid) impregnated with a chromate salt.Where the light strikes the gelatine it is rendered nearly unswellableby water. The exposed gelatine plate is moistened with water (byimmersion or otherwise) for 10 to 30 of cellulosic bases of varyingviscosities.

bulk of the viscous liquid composition gradually pushed forward towardthe other end of the gelatine plate and the excess of the liquidcomposition finally pushed out and discarded. The moldable compositionis then allowed to harden and set to the final product. The timerequired for solidification of the composition depends upon theviscosity and air conditions but averages approximately 10 minutes.

The backing sheet with the solidified material immutably adheringthereto constitutes the printing plate and the whole is now strippedfrom the gelatine relief plate and allowed to com- 1 pletely solidify byexposure to the air for several hours. It is then ready to be put on aroll and rotogravure printing begun. Either half tone or intaglioprinting plates may be made by following the above general procedure,using of course the proper type of screen as recognized by those skilledin the art.

I have found that cellulose nitr'ate or cellulose acetate constitutes anexcellent base material. A composition which runs approximately 25% ofthe cellulose ester provides a finished printing material of greathardness and durability. In general the greater the precentage ofcellulosic base (considering the solids exclusive of $01- vents) thatcan conveniently be used without destroying the necessary initialmolding plasticity of the product the greater will be the hardness anddurability of the finished solidified product. I have found that acomposition made from a cellulosic base of low viscosity does not makeas hard a materialas a composition made from a cellulosic base ofrelatively high viscosity, but the hardest material is made from amixture In order to get a plastic which will flow at the desired ratefor molding purposes when a particular solvent is used and to obtain aliquid composition containing total solids of 20% to 35% or more, it ispreferable to use a mixture of cellulosic bases of varying viscosities.Such a mixture may comprise part -second cellulose nitrate and partcellulose nitrate of a high viscosity, such as part 4-secorld cellulosenitrate and part LO-second cellulose nitrate. Cellulose acetate alsoconstitutes a valuable cellulosic base material.

I have found that, as a rule, plasticizers, and particularlyplasticizers such as camphor, castor oil and the like, have a tendencyto decrease the hardness of the finished product. It is necessary,however, to add some plasticizer to the ingredients used in order thatthe composition be sufficiently plastic for initial molding purposes.

Preferred plasticizers for cellulose nitrate are tricresyl phosphate,triphenyl phosphate, or dibutyl phthalate, and for the cellulose acetate.1 find that triacetin is a satisfactory plasticizer.

As solvents for the cellulosic base, acetone,

ethyl acetate, butyl acetate, amyl acetate, butyl alcohol and similarwell-known solvents in commercial use may be used. To obtain the bestresults, the solvent which should be used will depend somewhat on theparticular cellulose base which is used. If cellulose nitrate is used asthe base material, I have found that ethyl acetate and butyl acetate areespecially valuable. Very effective results, where cellulose nitrate isused, can be obtained by using a mixture of two solvents, i. e.,technical butyl acetate this contains some butyl alcohol) and ethylacetate. If a material possessing very rapid setting and hardeningcharacteristics is desired, ethyl acetate also serves as an excellentsolvent. However, if a material possessing great hardness, sharpness anddurability is desired, as for example a material initially moldable toform a printing plate for fine detailed printing, I prefer to use amixture of butyl acetate and butyl alcohol with a small amount of ethylacetate added. Pure ethyl acetate is a less desirable solvent where afine printing form is to be made since the fine imprints and detailscarried by the copy relief are not so accurately and sharply copied byan initially plastic 'cellulosic composition having ethyl acetate as thesole solvent. Furthermore, ethyl acetate evaporates very quickly withcorresponding rapid hardening of the plate. Where quick hardeningis amajor consideration, and where exact impressions are not of primaryimportance, ethyl acetate provides an excellent solvent. Acetone andamyl acetate have proven to be particularly valuable solvents wherecellulose acetate is used as a base material.

All the materials should be as free from water as possible. Anyappreciable amount of water in the ingredients used greatly decreasesthe solubility of the cellulosic base. The commercial products mentionedare, however, normally free from water, so that no difficulty isencountered in obtaining materials capable of forming a composition ofdesired characteristics.

My preferred composition when in liquid form contains 12 to of totalsolids and 65 to 80% of solvents. The solids comprise preferablycellulose nitrate or acetate, with a small amount of plasticizer added.I have found that a'mixture of cellulose nitrate material of varyingviscosities generally produces a harder, tougher and more desirablehardened product. The mixtures of cellulose nitrate should be soselected as to achieve this end. An excellent mixture comprises V secondcellulose nitrate approximately 50%, 4 second cellulose nitrateapproximately 10%, and 40 second cellulose nitrate approximately 40% Anyof these amounts might be increased with corresponding reductions in theothers. As plasticizers, I have found triphenyl phosphate or tricresylphosphate or dibutyl phthalate to be among the best and should be usedin small or moderate percentages, of from 1 to 5% of thetotalcomposition. As solvents, mixtures of com mercial butyl acetate andethyl acetate seem to be the best, but amyl acetate may also be used.Commercial butyl acetate generally carries about 20% butyl alcohol,which is not objectionable. A small amount of benzene or similar cheapersolvent may be used to reduce the cost.

The particular portions and ingredients which we have found to beespecially valuable may be described as follows:

Example 1 A composition giving a printing plate of great hardness anddurability and which will faithfully *copy the finest surfaceimpressions may be made from a mixture comprising 25% by weight of totalsolids and 75% by weight of solvents. The total solids comprise 20%triphenyl phosphate, 20% 40 second cellulose nitrate, and 60% /2 secondcellulose nitrate. The solvent used comprises a mixture of 58% amylacetate and 42% butyl acetate. Giving the quantities by weight and intotal percentages, this composition comprises 15% /2 second cellulosenitrate, 5% 40 .percentages, this composition comprises 10% secondcellulose nitrate, 10% 40 second cellulose nitrate, 5% triphenylphosphate, 43.5% amyl acetate and 31.5% butyl acetate. This compositionhas a viscosity of 70 seconds (by falling ball test).

Example 3 A composition comprising 25% by weight of solids and 75% byweight of solvents. The solids comprise 5% tricresyl phosphate, 71%second cellulose nitrate, and 24% 40 second cellulose nitrate. Thesolvent used is ethyl acetate unmixed with any other material. Givingthe quantities by weight and in total percentages this compositioncomprises 17.75% V: second cellulose nitrate, 6% 40 second cellulosenitrate, 1.25% tricresyl phosphate and 75% ethyl acetate. Thiscomposition has a viscosity of 39 seconds (by falling ball test).

Example 4 A composition comprising 25% by weight of solids and 75% byweight of solvents. The total solids comprise a mixture of 5% tricresylphosphate and of cellulose acetate (60% of 15 second cellulose acetateand 40% of 5 second eellulose acetate). The solids above described aredissolved in a mixture of equal proportions of methyl acetate andacetone. Giving the quantitles by weight and in total percentages, thiscomposition comprises 23.75% of cellulose acetate, 1.25% tricresylphosphate and 75% mixed substantially self sustaining and a mass of themasolvent. The composition as above named has a viscosity of '70 seconds(by falling ball test).

Example 5 A composition comprising total solids 35.6% by weight andsolvents 64.4% by weight. The

total solids comprise 5.2% triphenyl phosphate,

8.3% gum dammar, 43.25% second cellulose nitrate, and 43.25% 40 secondcellulose nitrate. The solvents used comprise 66.1% butyl acetate, 27.8%ethyl acetate and 6.1% of gum dammar solvents. The solvents for the gumdammar comprise 42% benzene, 9.2% ethyl acetate, 8.1% acetone and 40.7%methyl alcohol. Giving the quantities by weight and in totalpercentages, this composition comprises 15.4% /2 second cellulosenitrate, 15.4% 40 second cellulose nitrate, 1.9% triphenyl phosphate,2.9% gum dammar, 42.6% butyl acetate (technical), 1'7 .9% ethyl acetate,and 3.9% gum dammer solvent. This composition has a viscosity of 800seconds (by falling ball test). It is noted that this material has ahigh viscosity and if, for certain purposes, it is found too viscous tomold properly, its viscosity can be lowered by adding butyl acetate orethyl acetate.

Example 6 A composition comprising total solids 20% by weight and 80% byweight of a solvent consisting of tetrachlorethane. The solids comprise5% of triacetin and 95% of equal amounts of 15 second and 1 secondcellulose acetate. Giving the quantities by weight in total percentages,this composition comprises 1% of triacetin, 19% of cellulose acetate and80% of tetrachlorethane. This composition has a viscosity of 50 seconds(by the falling ball test).

Where the composition is composed of only cellulose nitrate or acetate,a plasticizer and a solvent, it does not matter in what orderthey aremixed. The resulting solution, however, requires some time and stirringbefore it reaches complete homogeneity. When completely dissolved andmixed, the material should be filtered and is then ready for use.

When a gum or resin'such as gum dammar is used, it is preferable todissolve the gum in its own solvent and later add this solution to thematerial above described. The gum solvent which should be selected willdepend upon the gum or resin chosen, but in general it will consist ofan anhydrous mixture of benzene, methyl alcohol and possibly othersolvents, such as.acetone and ethyl acetate. The gum solution is addedto the cellulose base solution and the two are mixed by stirringtogether. The final material is filtered and is then ready for use.

The moldable composition which is to be applied to the gelatine copyrelief, as noted above, is very viscous. It has been found that thepreferred viscosity is such that the material, while moldable, is not ofitself freely flowable (like a spraying or brushing lacquer) butrequires a considerable degree of mechanical pressure to force it intothe fine macroscopic depressions of the copy relief. On the one hand the'material should be sufflciently fiowable to be forced into suchdepressions and on the other" hand must not be so fluid as to freelyenter such depressions. In the latter case, as where the material has ahigh percentage of solvents, subse quent evaporationof the solventcauses shrinkage of the mass during the hardening process, resulting inpoor work. The material employed in actual practice is of such viscositythat it is terial placed on a swollen-gelatine sheet would not, withinany reasonable time, flow over the sheet. The viscosity characteristicsare therefore of salient importance.

The finished material generally is semi-trans- I parent and watercolored. It may be found desirable in certain instances to give themateriala distinctive color. I have found, for example, that thematerial can be colored without harm thereby by adding a coloringmaterial dissolved in asuitable solvent. for example, .01 g. of oil red,or oil orange, or other color, dissolved in 5 cc. of ethyl acetate.

My compositon material gives a product which is only slightlythermoplastic and hardens first by absorption of the solvent by thebacking sheet (if one is used), secondly by precipitation processes whenthe plastic composition material contacts with the moisture and watercarried by the water swollen gelatine copy relief, and finally, byevaporation of the residual solvent through exposure of the material tothe air.

As many changes can be made in the steps and ingredients used withoutdeparting from the scope of my invention, it is intended that all mattercontained in the above description shall be interpreted as illustrativeand not ina limiting sense.

What I claim is:

1. 'A moldable composition for forming printing plates, comprising aplurality of cellulose acetate materials of differential viscosity, aminor proportion of a plasticizer, the whole being dissolved in anorganic solvent, the composition having a viscosity in excess of 10seconds.

2. A hardenable composition for printing plates and the like, comprisingcellulose acetate materials of difierential viscosity, a resinoid, asmall quantity of a plasticizer, and a suflicient quantity of a volatilesolvent to render the mass workable, the composition having a viscosityin excess of 10 seconds.

3. A hardenable composition for printing plates and the like, comprisingcellulose acetate materials of differential viscosity, a relativelysmall amount of tricresyl phosphate, and a ketonic solvent, thecomposition having a viscosity in excess of 10 seconds.

4. A moldable composition for forming printing plates comprising aplurality of cellulose acetate materials of differential viscosity and asmall amount of a plasticizer dissolved in a volatile solvent, thecomposition having a viscosity greater than 50 seconds (by falling balltest).

5. A moldable composition for forming printing plates comprising aplurality of cellulose acetate materials of differential viscosity and asmall amount of a plasticizer dissolved in a 'volatile solvent, thecomposition having a viscosity of between 50 and 70 seconds (by fallingball test).

6. A moldable composition for forming printing plates comprising amixture of cellulose acetates of difierential viscosity, a small amountof a plasticizer comprising an amount not more' than 5% of the celluloseacetate base and a volatile solvent, and having a viscosity of between50 and '70 seconds (by falling ball test.)

7. A moldable composition for forming printing plates comprising, aplurality of cellulose acetate materials of differential viscosity, aplasticizer added in such minor proportions as not to substantiallydecrease the hardness of the finished product, the whole being dissolvedin an organic solvent, the composition having a viscosity substantiallyin excess 01 seconds, whereby mechanical pressure is required to forcethe composition into impressions of the order of those obtained in asensitized water swollen gelatin copy reliei'.

8. A potentially hardenable composition for the manufacture of printingplates comprising, a major percentage of a plurality of celluloseacetate materials of diflerential viscosity, minor percentages of asuitable plasticizer and a resinoid, and a suiiicient quantityoivolatile solvent to render the mass moldable, the composition having aviscosity in excess of 50 seconds, whereby mechanical pressure isrequired to force the composition into impressions of the order of thoseobtained in a sensitized water swollen gelatin copy relief.

9. A hardenable composition for making printing plates comprising, aplurality of cellulose acetate esters of diflerential viscosity,v aresinoid, a small quantity of a plasticizer, and a suflicient quantityof a volatile solvent to render the mass workable, the compositionhaving a viscosity sub- .stantially greater than 10 seconds.

10. An improved printing plate comprising. a

cellulose acetate base and a plasticizer, the cellulose acetateincluding a plurality of cellulose acetate compositions of diflerentviscosity, the plasticizer comprising an amount not more than 5% 01' thecellulose acetate base.

assaasocomposition having a viscosity in excess oi 10 seconds, thetricresyl phosphate comprising an amount not more than 5% o! thecellulose acetate base.

12. A hardenable composition for making printing plates including, aplurality of cellulose acetates of diflerential viscosity, a minorproportion of tricresyl phosphate, and a sufllcient quantity of avolatile organic solvent to render the mass workable, the compositionhaving a viscosity in excess of '10 seconds.

13. A hardenable composition for making printing plates including, aplurality of cellulose acetates of varying viscosity, 9. minorproportion 01' triacetin, and a sui'iicient quantity of a volatilesolvent to render the mass workable, the composition having a viscosityin excess of 10 seconds.

14. A hardenable composition for making printing plates comprising, aplurality of cellulose acetates of differentialviscosity, a smallquantity of a plasticizer, and a suillcient quantity of tetrachlorethaneto render the mas workable, the composition having a viscosity in excessof 10 seconds.

RALPH H. McKEE.

